Sound reproducer



Dec. 1, 19.31.

H. R. PARSHALL 1,834,498

SOUND REPRODUCER Filed March 10, 1930 MIA/[6 -40 200 40a 600 800 0 mpInuemlur BITE;

Fatented Dec. ll, $.93

rent

Application filed Ziarch 1Q, 1930. Serial Iil'o. 434,483.

My invention relates in general. to a sound reproducer or loud speakeremploying the Joule efiect or the linear e ansion and contraction of ametalic rod no to magneto- 6 striction to o crate a diaphragm.

More speci cally, my invention consists of a reproducer having adiaphragm or cone directly connected to one end of a metallic rod, theother end of which is firmly fixed, and in 19 causing variations in themagnetic flux in this said rod and consequent variations in the lengththereof to effectively operate the cone to re reduce sound.

h agnetostriction was first discovered in 1837 by Dr. C. G. Page and isa term applied to changes in dimension of a magnetic metal when placedin a magnetic field. Experiments brou ht to light the changes in lineardimension commonly called the Joule effect) due to variations in themagnetic flux, and also various other henomena such as twisting effectsupon the metal were observed, but very little was done toward applyingthis phenomena to any practical use.

All ferromagnetic metals are found to expand and contract when placedunder the inliuence of a varying magnetic field by virtue of theirmagnetostrictive properties. Iron first expands, then returns to its ori'nal length and then contracts in a longitu 'nal magnetic field ofincreasing strength. Pure iron and steels which are alloys of iron andcarbon although. strongy magnetic show weak magnetostrictive e ects.Cobalt first contracts, then returns to its original length and thenexpands, while annealed cobalt con tracts continually. Pure nickelcontracts continually and has strong magnetostrictive qualities. Certainallo s such as nickel (36%) and iron (644753 are active, while among themost active metals readily obtainable are alloys of chromium, nickel andiron, such as nichrome and Monel metal.

It has also been noted that heat treatment,

twisting, or stretching, increase the magnetostrictive qualities ofcertain metals and l have also observed that ageing by electricalvibration increases the action. It has been noted that the curverepresenting the change in length of a metallic rod is not constant.

Fig. l of the drawings shows the curve of iron and nickel, and isthought to be selfexplanatoig. V

Fig. 2 s ows the construction of the reproducer of my improved design insomeas what diagrammatic form.

Referring to Fig. 1, it Will be noted that nlckel, which contractssteadily with increasing magnetism, has a point between a and b m whichmagnetic variations of given to amount produce the greatest changes inlength. In my improved reproducer I propose to use a metallic rod ofnickel ,or of invar and good results have been obtained with both. Inorder to utilize the most oiled. tive portion of the magnetostrictivecurve I employ a strong permanent magnet such as shown in Fig. 2, or anelectroma et, to polarize the rod and to bring it wi the sensitive orefi'ective portion of this curve so that any given change in the currentthrough the coil around the rod will cause the greatest change in lengthof the rod and consequentl the maximum volume in the reproducer. hods ofdifi'erent metal and 15 length will require magnets of different stren11.

Re erring now to the illustration of my invention shown on theaccompanying drawings in Fig. 2, I have shown an ordinary cone ofstandard type at 1 having attached to its apex in known manner ametallic rod 2 which is rigidly held at its opposite end by a metallicstud 3 which has a split sleeve on its right hand end over which the nut4 fits to clamp against rod 2. The stud 3 clamps a collar 5 against anupright support 7 and secures a permanent magnet 6 between the uprightand the shoulder of stud 3. The coil 8 is wound on a fibre sleeve 9 andhas spool heads 10 and 11 and terminals 12 and 13 which are connectedwith the alternating current output of a radio receiving set. Each endof sleeve 9 has a metallic sleeve at 14 and 15 which are held in collars5 and 16 by set screws. The hollow screw 17 clamps the collar 16, magnet6, and support 18 together. Thus the entire assembly is rigidly heldtogether and magnet 6 magnetizes rod 2 to a point above zero andpreferably to the point 1 of magnetism between points a and b on thecurve shown in Fig. l.

The use of magnet 6 is not only to magnetize the rod to its eficientpoint of the curve but to polarize the rod as explained. It isunderstood that the flux in the rod must not pass through zero. Asalternating current from the secondary of a transformer is received fromthe ordinary commercial receivin 0; set instead of undulating current,the premagnetization by magnet 6 causes changes in flux due toalternating current cycles through electromagnet 8 to only increase anddecrease the flux through the rod 2 above the zero point. It should beunderstood that an electromagnet may be employed in place of permanentmagnet 6 and may be excited either by the plate current from the radioset or by a separate source of direct current.

If such electromagnet were used then an element or elements or soft ironor the like would be used in place of the permanent magnet 6 to providethe return path for the magnetic flux, and also to maintain the rigidityof the structure. In such case, as in the case of the permanent magnet,the magnetostrictive changes in the iron of the ma et or the elementsabove mentioned may o bourse be opposite to the changes in the rod 2,depending upon the materials, used in the construction of the rod andmagnet. In case the ma terials have opposite magnetostrictivecharacteristics, then the contrary action of the iron supporting frame18 and the nickel element or rod connected to diaphragm would becumulative in effect on the diaphragm..

It should be noted that a strong magnetic field (800 gauss) orapproximately 30 amperes of current is required to completely expand orcontract a rod bymagnetostriction. The reproduced sounds will beincreased 800 times, by the use of a permanent magnet, over thoseproduced by weak voice currents only, if the rod is not premagnetized.Therefore, in a construction such as shown I have produced a reproducerwhich gives a greater volume of sound, free from distortion, than hasbeen produced before.

While I have described the expansible element of the speaker as ametallic rod 2, it should be understood that this term is used and a rodshown merely for illustration and the'element may assume difierentdimensions. It is only necessary that it be a member of metal or alloyedmetal of greater length-than diameter acted upon by a coil to producelinear expansion and premagnetizedor polarized by a magnet. Furthermore,as the rod or movable element of the reproducer will have practically noaudible frequency or natural vibration of its own, and as the lag inmagnetostriction is practically nil, the reproduction will be accurateand without distortion.

Although I have shown a cone speaker with free edges, it should beunderstood that any type of cone or diaphragm may be used, and also anyknown leverage arrangement may be utilized between the rod and cone asdesired.

What is claimed is:

1. In a sound reproducer, a metallic rod having strong magnetostrictiv'equalities, an electromagnet encircling said rod and spaced slightlytherefrom, a strong permanent magnet arranged with opposite polesthereof opposite diflerent ends of the rod, a clamping means rigidlysecuring one end of the rod, a

diaphragm connected to the opposite end of the rod, said coil whenconnected to alternating current effective to vibrate the diaphragm inaccordance with the current.

2. In a sound reproducer, a vibratory memher, an actuating element forthe member constructed of ferro-magnetic metal having strongmagnetostrictive qualities, said element rigidly secured at one end andattached at the other end to the vibratory member, a permanent magnet ofrelatively large and predetermined strength arranged longitudinally tosaid element, said magnet premagnetizing said element to its mosteflicient point of sensitivity to magnetostrictive variations, a helixor electromagnet encircling said element for the greater part of itslength, said helix connected to a sourceof alternating current to causecorresponding lineal expansion and contraction of said element tothereby vibrate said member.

3. In a sound reproducer, a ferro-magnetic member, specifically treatedto increase its lineal displacement due to magnetostrictive effects, an'elongated U-shaped permanent magnet of predetermined strength, saidmember longitudinally supported in the magnetic field of said permanentmagnet, one pole of the magnet in magnetic contact with the member atone rigidly fixed extremity, the other pole in close proximity but outof engagement with the member providing a return path for magnetic fluxin the member with minimum air gap, a diaphragm connected to one end ofthe member, an electromagnot associated with the member connected withthe output of a suitable audible frequency sound amplifier, saidelectromagnet nee-sees of the actuating member and rigidly secun ing itto the permanent magnet, a frame supporting the diaphragm, a hollowsleeve often ro-magnetic metal securing the frame to the permanentmagnet to the free end of said member extending through said hollowsleeve and secured to the center of the diaphragm,

said helix when connected to a source of alternating current causingvibrations of the diaphragm in accordance with current changes.

' anelectromagnet arranged longitudinally to i 5. In a sound reproducer,a vibrating element, an actuating member therefor, a per= manent magnet,an operating member of ferire-magnetic material having strongmagnetostrietive qualities supported by the magnet and rigidly securedthereto at one en a frame supporting the vibrating element rigidlysecured to the other end of the magnet, said operating member extendingthrough an opening in one end of-the permanent ma et and engaging saidvibrating member, an an electromagnet for varying the effectof saidpermanent magnet on said operating member to vibrate the element, saidmagnetic member and element forming a unitary structure.

6. In a sound reproducer, a diaphragm a permanent magnet, an operatingmember or the diaphragm of ferro-ma etic material havingmagnetostrictive qualities 0 posite to that of said permanent magnet,sai member rigidly supported and in magnetic contact with one linch ofthe magnet and having its free end encircled by the other linch of saidmagnet, and engaging with the die. hragm,

both magnet and member and connectedto a source of variable current,variations in current in the electromagnet causing oppositemagnetostrictive efiects in the member and magnet cumulative in theirefiect on the diaphragm.

In witness whereof, I hereunto subscribe iny-name this 7th day of MarchA. D. 1930. RRY R. i. i

